1. Field of the Invention
The invention is directed to a self cleaning roller chain sprocket having a plurality of radially extending teeth between which are formed a receiving pocket for a chain roller and inwardly thereof is a foreign material receiving niche for receiving foreign material forced therein by the chain roller. A chain drive using this sprocket is particularly well suited for use in an agricultural machine such as a planter.
2. Description of the Prior Art
Sprocket and chain transmission systems are well known in the art and are used in a great variety of machines. Typically, the sprockets are circular metal discs having a plurality of radially extending teeth in which adjacent pairs of teeth form chain roller engaging pockets. The chain comprises a plurality of connecting links between which are mounted a plurality of chain rollers which are received in the sprocket grooves. The American National Standards Institute (ANSI) has formulated standards for designing sprockets based on chain pitch, number of teeth, and chain roller diameter. Typically, ANSI designed sprockets are quite reliable for transmitting motion.
However, when ANSI designed sprockets are used in a harsh and dirty environments, such as in agricultural machinery, they tend to collect foreign material, such as dirt and stalks, which can significantly hinder their performance and endurance. Dirt interfering with the sprockets can lead to two common malfunctions, "jumping" and "wedging". Jumping is the tendency of the chain to jump to climb teeth and may result from the buildup of foreign material in the tooth pocket resulting in an oversized effective bottom diameter. Wedging of the chain over opposite faces of the sprocket teeth results in greater chain tension and can lead to breakage of the sprocket, chain or support bearings. Traditionally, one method for overcoming these problems has been to undersize the bottom diameter of the sprocket to accommodate foreign material buildup. However, this reduces the effective diameter of the sprocket and shifts the chain roller point of contact with the sprocket inwardly. In addition, a pitch line clearance allowance may be added to allow foreign material to work out of the tooth pocket as the chain roller is forced into the tooth pocket. Motorcross riders have been known to file standard sprocket pockets down apparently to better accommodate dirt trapped in the sprocket. However, generally the effect of such filing is the same as the above described undersized bottom diameter.
Traditionally designed chain sprockets have not proved to be entirely satisfactory in agricultural machines, especially planters, because of the nature of their environment. Dirt, stalks and other agricultural material comes into contact with the sprockets resulting in inefficient transfer of energy from or to the sprockets and the chain and may result in breakage of the sprocket.